Context. Ultrapure water factory in Emmen (Netherlands) utilizes Biological Oxygen-dosed Activated Carbon (BODAC) filters to produce ultrapure water from wastewater. BODAC filters comprised of a series of five pre- and post-filters, regularly flushed with oxygen, and have been continuously operated for more than ten years without carbon replacement/re-activation. BODAC filters are periodically backwashed to avoid biofilm overgrowth and remove excess solids. The filters are effective in removing some organic (micro)pollutants (OMPs) to a high extent (up to 90%), but backwashing may hamper their performance.
Gap. The effect of backwashing on the performance and the microbial community profile of the filters has never been elucidated before.
Aim. To determine the microbial groups that are strongly adhere to the BODAC granules and their potential role(s) in catalyzing nitrification and OMPs removal in BODAC filters.
Methods. The influent and effluent water were analyzed for ionic and OMPs concentrations via ion chromatography and LS-MS/MS. DNA extracted from BODAC carbon granules, sampled before and after backwashing, was analyzed via Next Generation Sequencing of 16S rRNA gene, and the data analyzed with statistical packages in R.
Findings. The backwashing had little influence on the ionic and OMPs profiles of the water samples, i.e. nitrification and removal of OMPs were still observed. The backwashing only slightly reduced the relative abundance of some dominant microbial groups, such as nitrifying bacteria. This means these dominant microbes are strongly adhered to the granule. Both findings suggest that the strongly adhered microbes are more likely involved in the processes taking place in the filters than the loosely-bound microbes.
Utilization. OMPs removal carried out by the microbial community associated with BODAC granules has the potential to be implemented as a bioremediation strategy in nutrient limited environments. Biofilms can support the BODAC performance and substantially extend the BODAC service life.
